Planar inductive component and a planar transformer

ABSTRACT

The invention relates to a planar inductive component ( 11 ) comprising at least a first and a second concentric inductor, which include a first and a second spiral pattern ( 12 A,  12 B), respectively. Both spiral patterns have a first end point ( 13 A,  13 B) and a second end point ( 14 A,  14 B), are electrically interconnected, interlaced, and interrupted at the outer side, and provided with two contacts ( 16 A,  16 B) on one side of the opening ( 15 A,  15 B) and two contacts ( 17 A,  17 B) on the other side of the opening ( 15 A,  15 B). By interconnecting the first two contacts ( 16 A,  16 B) and the second two contacts ( 17 A,  17 B), respectively, both spiral patterns are connected in parallel. The spiral patterns ( 12 A,  12 B), which are magnetically coupled, have identical electrical and magnetic properties. This leads to a reduction of eddy current losses at high frequencies. This results in a planar inductive component ( 11 ) which is suitable for high-frequency operation with a high maximum quality factor Q. The invention also relates to a planar transformer comprising two planar inductive components according to the invention. The first planar inductive component serves as the first winding of the planar transformer; the second planar inductive component serves as the second winding of the planar transformer. As a result of the above-mentioned reduction in eddy current losses at high frequencies, the planar transformer can suitable be used for high-frequency operation.

The invention relates to a planar inductive component comprising atleast a first and a second concentric planar inductor, which include,respectively, a first electroconductive spiral pattern and a secondelectroconductive spiral pattern, the first electroconductive spiralpattern having a first end point and a second end point, and the secondelectroconductive spiral pattern having a first end point and a secondend point.

The invention also relates to a planar transformer comprising a firstsuch planar inductive component and a second such planar inductivecomponent.

In the course of time, integration in electronics has increasedsubstantially, enabling more and more functions to be integrated in anever decreasing volume. This integration has also been made possible bythe advances made in the field of, for example, assembly techniques andIC technology. The advances made in the field of IC technology incombination with the demand for electronic products in the field ofcommunication, for example in the field of mobile telephones, have ledto integrated RF circuits (radio frequency circuits) wherein planarinductive components, such as inductors and transformers, are used. Thefrequency bands used in, for example, mobile telephony, such as the 900MHz and the 1800 MHz bands, enable these planar inductive components tobe readily and reproducibly manufactured in existing technologiestogether with other components on one integrated circuit.

A problem with such planar inductive components is the reduction of theohmic losses to a minimum. At high frequencies, the ohmic lossesincrease rapidly, while the (self-)inductance hardly changes. Thismeans, for example, that it is difficult to make good planar inductorsfor RF applications. In general, a good inductor is defined as aninductor having a quality factor above 10. This means that the ratiobetween the imaginary part of the impedance and the real part of theimpedance is equal to or larger than 10. Customarily, a planar inductorcomprises an electric conductor extending in accordance with a spiralpattern.

From the existing literature it is known that at frequencies in therange between 1 and 2 GHz, the inhomogeneous current distribution in aplanar magnetic inductor contributes substantially to the ohmic losses(reference is made to, for example, W. B. Kuhn, N. M. Ibrahim, “Analysisof current crowding effects in multiturn spiral inductors”, IEEE Trans.MTT, Vol. 49, No. 1, pp. 31-38, 2001). The electrical behavior of suchan inductor can be represented essentially by means of a seriesarrangement of a self-inductance L_(S) and a resistor R_(S). In thisseries arrangement, L_(S) represents the inductance of the spiralpattern and R_(S) represents the ohmic losses that occur in the spiralpattern. As regards the above-mentioned frequency range, the ohmiclosses are determined substantially by eddy current losses caused by theskin effect, and eddy current losses resulting from the mutual influenceof the juxtaposed turns in the spiral pattern.

In U.S. Pat. No. 5,966,063 a solution is proposed to limit eddy currentlosses in a planar inductive component. The basic embodiment of thesolution proposed is comprised of a planar inductive component having anelectric conductor extending in accordance with a spiral pattern, whichconductor is divided in the longitudinal direction into at least twoparts. As a result, the planar inductive components disclosed in U.S.Pat. No. 5,966,063 is comprised of at least two interleaved spiralpatterns. The innermost spiral pattern has a smaller length and asmaller surface area than the outermost spiral pattern. As a result, theelectrical and magnetic behavior of both spiral patterns are different.Consequently, the solution described in U.S. Pat. No. 5,966,063 onlypartly solves the problem of ohmic losses caused by eddy currents.

It is an object of the invention to provide a planar inductive componentwhose ohmic losses caused by eddy currents are low. This object isachieved by means of a planar inductive component in accordance with theinvention, characterized in that

the first electroconductive spiral pattern that belongs to the firstconcentric inductor, and the second electroconductive spiral patternthat belongs to the second concentric inductor are interlaced;

the first end point and the second end point of the firstelectroconductive spiral pattern are electroconductively interconnected,and the first electroconductive spiral pattern is interrupted at theoutside so as to form a first electroconductive contact and a secondelectroconductive contact on either side of the interruption;

the first end point and the second end point of the secondelectroconductive spiral pattern are electroconductively interconnected,and the second electroconductive spiral pattern is interrupted at theoutside so as to form a first electroconductive contact and a secondelectroconductive contact on either side of the interruption.

The first and the second planar inductor both comprise a spiral patternand are concentric. This means that they have a common imaginary center.

The first electroconductive spiral pattern that belongs to the firstconcentric inductor, and the second electroconductive spiral patternthat belongs to the second concentric planar inductor are interlaced.This means that moving from the imaginary center in a straight linetowards the periphery the first inductor and the second inductor alwaysalternate with each other.

The first and the second electroconductive spiral pattern each have afirst and a second end point. The first end point is the end pointclosest to the imaginary center, the second end point is the end pointthat is farthest removed from the imaginary center.

The spiral pattern of the first and the second concentric planarinductor is interrupted at the outside. “Interrupted at the outside”means that the interruption can be approached by moving in a straightline from a point situated outside the spiral pattern, yet in the planewherein the spiral pattern is situated, towards the imaginary center.

The spiral pattern of the first and the second concentric planarinductor is provided with a first electroconductive contact on one sideof the interruption, and with a second electroconductive contact on theother side of the interruption. The current path between the first andthe second electroconductive contact will thus comprise the entirelength of the spiral pattern of either the first or the secondconcentric planar inductor.

The advantage of the spiral patterns designed as described above residesin that these spiral patterns have the same magnetic and electricalproperties.

As a result, the current distribution is homogeneous. This results inlow ohmic losses.

A further advantage of the use of a spiral pattern resides in that itenables the highest possible (self-)inductance to be realized on thesmallest possible surface area.

Although the planar inductive component in accordance with the inventionis excellently suited for use within integrated circuits operating athigh frequencies, such as RF circuits on, for example, a siliconsubstrate, the application is not limited thereto. Other possibleapplications are, for example, in the field of switch-mode powersupplies. In the frequency range associated with these switch-mode powersupplies, it is favorable to realize such planar inductive componentson, for example, ceramic substrates by means of thin-film or thick-filmtechniques. Such planar inductive components can alternatively berealized as part of a circuit on a PCB (printed circuit board), in whichcase the spiral patterns are formed by, for example, copper tracks.

It may also be favorable to provide the planar inductive component withan envelope of a magnetic material to further improve the magneticproperties, provided that this is compatible with the technology used.

In addition, it may be possible that the design rules employed in acertain technology limit the designer to the use of patterns thatinclude angles of, for example, 45 or 90 degrees with each other. Insuch cases, the spiral pattern may be rectangular or octagonal inappearance.

An additional advantage of the planar inductive component in accordancewith the invention resides in that it can be used as a basic element inan assembly of planar inductive components. Such an assembly comprises aplurality of planar inductive components in accordance with theinvention that are arranged in the flat plane. By electroconductivelyinterconnecting said planar inductive components, a new, composite,planar inductive component is obtained whose electrical and magneticproperties can be accurately predetermined by means of the electricaland magnetic properties of a single planar magnetic component.

An embodiment of the planar inductive component in accordance with theinvention is characterized in that the planar inductors each comprise atleast a first electroconductive spiral pattern and a secondelectroconductive spiral pattern which are separated from each other byan electrically insulating layer. By using a plurality ofelectroconductive spiral patterns, a limitation of the necessary surfaceof the planar inductive component is achieved.

A further embodiment of the planar inductive component in accordancewith the invention is characterized in that at least the firstelectroconductive spiral pattern and the second electroconductive spiralpattern are electroconductively interconnected by vias. By electricallyinterconnecting a plurality of electroconductive spiral patterns anincrease of the effective section of the spiral patterns is achieved.This has the advantage that a smaller series resistance in combinationwith an unchanged (self-)inductance is achieved.

A further embodiment of the planar inductive component in accordancewith the invention is characterized in that the first electroconductivecontact of the first electroconductive spiral pattern iselectroconductively connected to the first electroconductive contact ofthe second electroconductive spiral pattern, and the secondelectroconductive contact of the first electroconductive spiral patternis electroconductively connected to the second electroconductive contactof the second electroconductive spiral pattern so as to form a system ofelectrically interconnected inductors having identical electrical andmagnetic properties. In this manner, an inductor is achieved that isdivided into a number of parallel current paths which are identical interms of their electrical and magnetic properties. As a result, also athigh frequencies, the current is equally distributed over the currentpaths. This has the advantage that the inductor has good high-frequencyproperties. This means that an inductor realized in this manner can havea quality factor above 10.

In the foregoing, the discussion focused mainly on planar inductors.Planar transformers have the same problems as planar inductors. In knownplanar transformers, the ohmic losses caused by eddy currents in thewindings increase substantially as the frequency increases. These ohmiclosses also limit the practical uses of known planar transformers athigh frequencies.

The invention also aims at providing a planar transformer having lowohmic losses. The planar transformer in accordance with the inventioncomprises a first planar inductive component in accordance with theinvention and a second inductive component in accordance with theinvention, wherein the first planar inductive component and the furtherplanar inductive component are separated by means of an electricallyinsulating layer, and wherein the first planar inductive component formsa first winding of the transformer and the second planar inductivecomponent forms a second winding of the transformer. A planartransformer thus realized has the advantage that in the first windingand in the second winding the current is equally distributed over thespiral patterns of the concentric planar inductors of the first planarinductive component and also equally distributed over the spiralpatterns of the concentric inductors of the second planar inductivecomponent. This results in low ohmic losses at high frequencies. As aresult, a good planar transformer suitable for operation at highfrequencies is achieved in this manner.

The planar transformer in accordance with the invention cannot only beused inside integrated circuits operating at high frequencies. It canalso be used, for example, in the field of switched-mode power supplies.In the frequency range associated with said switch-mode power supplies,such planar transformers are favorably realized, for example, on ceramicsubstrates by means of thin-film or thick-film techniques. Such planartransformers can alternatively be realized as a part of a circuit on aPCB, in which case the spiral patterns are formed by, for example,copper tracks.

It may also be favorable to provide the planar transformer with anenvelope of a magnetic material in order to improve the magneticproperties, provided that this is compatible with the technology used.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1A diagrammatically shows an embodiment of a planar inductor inaccordance with the prior art;

FIG. 1B shows an electrical equivalent-circuit diagram of the embodimentof the planar inductor shown in FIG. 1A;

FIG. 2A diagrammatically shows a different embodiment of a planarinductor in accordance with the state of the art;

FIG. 2B shows an electrical equivalent-circuit diagram of the embodimentof the planar inductor shown in FIG. 2A;

FIG. 3A diagrammatically shows an embodiment of a planar inductivecomponent in accordance with the invention;

FIG. 3B shows an electrical equivalent-circuit diagram of the embodimentof the planar inductive component shown in FIG. 3A;

FIG. 4 shows a graph wherein the improvement of the quality factorcalculated for an embodiment of the planar inductive component inaccordance with the invention is shown;

FIG. 5A is a diagrammatic cross-sectional view of an embodiment of theplanar inductive component in accordance with the invention;

FIG. 5B is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component in accordance with the invention;

FIG. 6A is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component in accordance with the invention;

FIG. 6B is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component in accordance with the invention;

FIG. 6C is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component in accordance with the invention;

FIG. 7 shows a part of a design of an integrated circuit comprisingthree planar inductors, including two embodiments of the planarinductive component in accordance with the invention;

FIG. 8 shows the measured quality factors as a function of the frequencyof the planar inductors shown in FIG. 7;

FIG. 9A is a diagrammatic cross-sectional view of an embodiment of aplanar transformer in accordance with the invention;

FIG. 9B is a diagrammatic cross-sectional view of a further embodimentof a planar transformer in accordance with the invention; and

FIG. 9C is a diagrammatic cross-sectional view of a further embodimentof a planar transformer in accordance with the invention.

In these Figures, like reference numerals refer to like parts.

FIG. 1A diagrammatically shows an embodiment of a planar inductor 1 inaccordance with the state of the art. In this embodiment, the planarinductor 1 is comprised of a spiral pattern 2 of electroconductivematerial that is provided on an electrically insulating layer of a basematerial or substrate. The spiral pattern 2 has a first end point 3 thatis closest to the imaginary center of the spiral pattern 2, and a secondend point 4 that is farthest removed from the imaginary center of thespiral pattern 2. At the location of the first end point 3 and thesecond end point 4, the planar inductor 1 is brought intoelectroconductive contact with further components of the circuit thatcomprises the planar inductor 1.

FIG. 1B shows an electrical equivalent-circuit diagram 5 of theembodiment of the planar inductor 1 shown in FIG. 1A. Said electricalequivalent-circuit diagram 5 is a one-gate element comprised of aself-inductance L_(S) that is arranged in series with a resistor R_(S).L_(S) represents the self-inductance of the spiral pattern and R_(S)represents the ohmic losses that occur in the spiral pattern. Theresistance characteristic of R_(S) is frequency-dependent. It is knownfrom the existing literature that at frequencies in the range between 1and 2 GHz, the inhomogeneous current distribution in a planar magneticinductor contributes substantially to the ohmic losses (reference ismade to, for example, W. B. Kuhn, N. M. Ibrahim, “Analysis of currentcrowding effects in multiturn spiral inductors”, IEEE Trans. MTT, Vol.49, No. 1, pp. 31-38, 2001). In this frequency range, the ohmic lossesare mainly determined by eddy current losses caused by the skin effectand eddy current losses caused by the mutual influence of the juxtaposedturns in the spiral pattern.

FIG. 2A diagrammatically shows a different embodiment of a planarinductor 6 in accordance with the state of the art. This embodimentrelates to the solution proposed in U.S. Pat. No. 5,966,063 to reduceohmic losses caused by eddy currents. The planar inductor 6 in thisembodiment consists of a spiral pattern 7 of electroconductive materialthat is provided on an electrically insulating substrate. The spiralpattern 7 is divided in the longitudinal direction into a first outsideportion 7A and a second inside portion 7B. Both portions 7A and 7B ofthe spiral pattern 7 are concentric and have a common first end point 8that is situated closest to the imaginary center of the spiral pattern 7and a second common end point 9 that is farthest removed from theimaginary center of the spiral pattern 7. The inside portion 7B of thespiral pattern 7 has a smaller length and a smaller surface area thanthe outside portion 7A. The term concentric is to be taken to mean thatboth spiral patterns 7A and 7B have a common imaginary center.

FIG. 2B shows an electrical equivalent-circuit diagram 10 of theembodiment of the planar inductor shown in FIG. 2A. Said electricalequivalent-circuit diagram 10 is a one-gate element comprising twoparallel branches. The first parallel branch comprises a firstself-inductance L_(S1) that is arranged in series with a resistorR_(S1). The second parallel branch comprises a second self-inductanceL_(S2) that is arranged in series with a resistor R_(S2). The firstparallel branch represents the electrical and magnetic behavior of theoutside portion 7A of the spiral pattern 7 shown in FIG. 2A. The secondparallel branch represents the electrical and magnetic behavior of theinside portion 7B of the spiral pattern 7 shown in FIG. 2A. As bothportions 7A and 7B of the spiral pattern 7 are closely spaced, theyinfluence one another. This magnetic coupling is represented by means ofthe coupling c between L_(S1) and L_(S2) in the electricalequivalent-circuit diagram 5.

At low frequencies, the ratio between the currents in both branches isdetermined by the ratio between the resistors R_(S1) and R_(S2). Ifthere was no coupling c between the two inductors, then, at highfrequencies, the ratio between currents through the inductors would bedetermined by the ratio between the self-inductances L_(S1) and L_(S2).In the planar inductor 6, as shown in FIG. 2A, there is a significantcoupling between L_(S1) and L_(S2), i.e. c≈1. If R_(S1) and R_(S2) areequal, it can be derived that, at high frequencies and differencesbetween L_(S1) and L_(S2) that are not too large, the actual part of thetotal impedance Z can roughly be given by the following relation:

$\frac{{Re}(Z)}{R} \approx {\frac{1}{2} + {\frac{1}{2} \cdot \frac{1}{\left( {1 - c} \right)^{2}} \cdot \frac{\left( {L_{S1} - L_{S2}} \right)^{2}}{\left( {L_{S1} + L_{S2}} \right)^{2}}}}$If the difference between L_(S1) and L_(S2) is larger and meets thefollowing relation

$\frac{{L_{S1} - L_{S2}}}{L_{S1} + L_{S2}} \geq {1 - c}$the magnetic coupling will lead, at high frequencies, to a currentreversal in the spiral pattern having the largest self-inductance.

The above-described behavior plays an important part in the planarinductor 6 if the width of the spiral patterns 7A and 7B amounts to 2 to10% of the overall diameter of the inductor 6. Calculations have shownthat the current in the spiral pattern 7B is subject to a smallerself-inductance than the current in spiral pattern 7A. It can also bedemonstrated that the current at the edges of the spiral patterns 7A and7B is subject to a lower self-inductance than the current in and nearthe center of the conductor.

In these cases, there is a strong coupling between the current paths.Dependent upon the width of the spiral patterns 7A and 7B, a substantialincrease of the real part of the impedance of the planar inductor 6 mayoccur. A reduction of the differences in self-inductance between thespiral patterns 7A and 7B by reducing the width of the spiral patternshowever leads to an increase of the resistance at low frequencies and,consequently, is not a satisfactory solution as it leads to a reductionof the quality factor Q.

FIG. 3A diagrammatically shows an embodiment of a planar inductivecomponent in accordance with the invention. Like the known planarinductor 6 described with reference to FIG. 2A, this embodiment of theplanar inductive component 11 in accordance with the invention comprisestwo concentric inductors. Both concentric inductors comprise spiralpatterns, a first spiral pattern 12A belonging to a first concentricinductor, and a second spiral pattern 12B belonging to a secondconcentric inductor. The spiral patterns 12A and 12B are made ofelectrically conductive material, and they comprise, respectively, firstend points 13A and 13B and second end points 14A and 14B, and they areprovided on an electrically insulating substrate. An importantdifference between the known planar inductor 6 and the inductivecomponent 11 resides in that the spiral patterns 12A and 12B areinterlaced. This means that moving from the imaginary center in astraight line towards the periphery, the first spiral pattern 12A andthe second spiral pattern 12B always alternate with each other.Furthermore, in each of the spiral patterns 12A, 12B, the first endpoint 13A, 13B is electroconductively connected to the second end point14A, 14B. Also each of the spiral patterns 12A, 12B is interrupted atits outside. This interruption serves to form a first electroconductivecontact 16A, 16B, respectively, on one side of the interruption 15A,15B, respectively, and a second electroconductive contact 17A, 17B,respectively, on the other side of the interruption 15A, 15B,respectively. In FIG. 3A, the first conductive contact 16A and thesecond conductive contact 17A of the spiral pattern 12A are situatedbelow the first conductive contact 16B and the second conductive contact17B of the spiral pattern 17B. The current path between the firstelectroconductive contact 16A, 16B and the second electroconductivecontact 17A, 17B, respectively, will consequently comprise the entirelength of the spiral pattern 12A or 12B of, respectively, the first orthe second concentric planar inductor. As a result, the electrical andmagnetic properties of both concentric inductors of the inductivecomponent 11 in accordance with the invention are identical.

FIG. 3B shows an electrical equivalent-circuit diagram 18 of theembodiment of the planar inductive component shown in FIG. 3A. In theembodiment shown in FIG. 3A, the first electroconductive contact 16A ofthe spiral pattern 12A is electroconductively connected to the firstelectroconductive contact 16B of the spiral pattern 12B. In addition,the second electroconductive contact 17A of the spiral pattern 12A iselectroconductively connected to the second electroconductive contact17B of the spiral pattern 12B. In this manner, both concentric inductorsof the inductive component are parallel-connected.

The electrical equivalent-circuit diagram 18 is a one-gate elementcomprising two identical parallel branches. As discussed hereinabove,both spiral patterns 12A and 12B shown in FIG. 3A are identical in termsof their electrical and magnetic behavior. Both parallel branches of theelectrical equivalent-circuit diagram 18 comprise a self-inductanceL_(S3) arranged in series with a resistor R_(S3). Each of the parallelbranches represents the electrical and magnetic behavior of one of thespiral patterns 12A and 12B shown in FIG. 3A. As both spiral patterns12A and 12B are closely spaced, they influence one another. Thismagnetic coupling is shown in the electrical equivalent-circuit diagram18 by means of the coupling c₁ between the two self-inductances L_(S3).

FIG. 4 graphically shows the improvement of the quality factor Q that iscalculated for an embodiment of the planar inductive component inaccordance with the invention, in this case a planar inductor. Saidplanar inductor has a self-inductance of 4 nH and a diameter of 300 μm.On a semi-logarithmic scale, n is plotted along the horizontal axis, nbeing the number of parallel arranged, interlaced concentric inductorsfrom which the planar inductive component is built up, and the maximumattainable quality factor, Q_(max), is plotted along the vertical axis.The graph shows that a significant improvement of Q_(max) is obtained ifn, i.e. the number of spiral patterns 12, is increased. At n=1, Q_(max)is 11.6, at n=32, Q_(max) has increased to 19.4. The graph of FIG. 4also shows that the greatest improvement is attained in the step fromn=1 to n=2, which is a clear illustration of the favorable effect of theinvention.

FIG. 5A is a diagrammatic cross-sectional view of an embodiment of theplanar inductive component 11 in accordance with the invention. Thisembodiment comprises a first and a second concentric, interlaced, planarinductor. The first concentric planar inductor comprises a first spiralpattern 19A and a second spiral pattern 19B. The second planar inductorcomprises a first spiral pattern 20A and a second spiral pattern 20B.The spiral patterns 19A, 19B, 20A, 20B are made of an electroconductivematerial. The first spiral patterns 19A, 20A are provided on thesubstrate 21. The first spiral patterns 19A, 20A and the second spiralpatterns 19B, 20B are separated from each other by a first electricallyinsulating layer 22A. In addition, a second electrically insulatinglayer 22B is shown that is provided over the second spiral patterns 19B,20B. The circles 23 and 24 indicate the current directions. The currentdirection is perpendicular to the cross-section. The circles 23 having adot in the center indicate that the current flows towards the reader.The circles 24 having a cross in the center indicate that the currentflows away from the reader. By using the first spiral patterns 19A, 20Aand the second spiral patterns 19B, 20B, a limitation of the necessarysurface area of the planar inductive component 11 is attained. Thisembodiment is particularly suitable for use in integrated circuits.

FIG. 5B is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component 11 in accordance with the invention.This embodiment is comparable to the embodiment shown in FIG. 5A. As inthe embodiment shown in FIG. 5A, the concentric, interlaced planarinductors comprise the first spiral pattern 19A, 20A and the secondspiral pattern 19B, 20B. This embodiment is very suitable for use inthin-film or thick-film technologies with, for example, a ceramicsubstrate on either side of which electroconductive thin-film materialsor thick-film materials are provided. This embodiment is alsoexcellently suited for use on printed circuit boards on either side ofwhich electroconductive layers of, for example, copper are provided. Thedifference relative to the embodiment shown in FIG. 5A resides in thatthe substrate 21 does not only serve as a support but also as anelectrically insulating layer.

FIG. 6A is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component 11 in accordance with the invention.This embodiment is comparable to the embodiment shown in FIG. 5A. As inthe embodiment shown in FIG. 5A, concentric, interlaced planar inductorscomprise a first spiral pattern 19A, 20A and a second spiral pattern19B, 20B.

The outstanding difference relative to the embodiment shown in FIG. 5Aresides in that the first spiral pattern 19A, 20A is electroconductivelyconnected to the second spiral pattern 19B, 20B by means of vias 25. Byelectroconductively connecting the first spiral pattern 19A, 20A to thesecond spiral pattern 19B, 20B, it is achieved that the effectivecross-section of the two concentric, interlaced planar inductors isincreased. This has the advantage that a smaller series resistance isachieved in combination with an unchanged self-inductance. A reductionof the series resistance achieved in this manner is important because inthe standard technologies that can be used to realize planar inductivecomponents in accordance with the invention, the thickness ofelectroconductive layers is predetermined, while these technologiesgenerally do afford the possibility of stacking a plurality ofelectroconductive layers in such a way that they are electricallyinsulated from each other. These conductive layers can then beinterconnected by means of vias in an electrically conducting manner.

FIG. 6B is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component 11 in accordance with the invention.This embodiment is comparable to the embodiment shown in FIG. 6A. As inthe embodiment shown in FIG. 6A, the concentric, interlaced planarinductors comprise the first spiral pattern 19A, 20A and the secondspiral pattern 19B, 20B. This embodiment is particularly suitable foruse in thin-film or thick-film technologies with, for example, a ceramicsubstrate on either side of which electroconductive thin-film materialsor thick-film materials are provided. This embodiment is alsoexcellently suited for use on printed circuit boards on either side ofwhich electroconductive layers of, for example, copper are provided. Thedifference relative to the embodiment shown in FIG. 6A resides in thatthe substrate 21 does not only serve as a support but also as anelectrically insulating layer.

FIG. 6C is a diagrammatic cross-sectional view of a further embodimentof the planar inductive component 11 in accordance with the invention.This embodiment is comparable to the embodiment shown in FIG. 6B. Theoutstanding difference is that the planar inductive component isprovided with an envelope 26 of magnetic material. The envelope 26comprises a first part 26A and a second part 26B. In cases where thetechnology used enables an envelope of magnetic material to be applied,said envelope has the advantage that the planar inductive component 11has improved magnetic properties. In practice, this leads to a higherquality factor Q. For practical reasons, for example to increase thereproducibility in mass-production, it may be useful to provide a small,well-defined air gap 27 between the first part 26A and the second part26B.

FIG. 7 shows a part of a design 28 of an integrated circuit comprisingthree embodiments of planar inductors, including two embodiments of theplanar inductive component in accordance with the invention. The design28 comprises an embodiment 29 of a planar inductor in accordance withthe state of the art, an embodiment 30 of the planar inductive componentin accordance with the invention with two concentric, interlaced spiralpatterns, and an embodiment 31 of the planar inductive component inaccordance with the invention with four concentric, interlaced spiralpatterns. In other respects, the three embodiments 29, 30, 31 in thedesign are designed so as to be as identical as possible. The design 28offers a manner of comparing the improved behavior at high frequenciesof the planar inductive components 30 and 31 in accordance with theinvention with the behavior at high frequencies of the planar inductor29 in accordance with the state of the art.

FIG. 8 shows the measured quality factors as a function of the frequencyof the planar inductors shown in FIG. 7. Curve 29A shows the measuredquality factor Q as a function of the frequency of the embodiment 29 ofa planar inductor in accordance with the state of the art. The maximumvalue of curve 29A is 11.3. Curve 30A shows the measured Q as a functionof the frequency of the embodiment 30 of the planar inductive componentin accordance with the invention. The maximum value of curve 30A is12.8. Curve 31A shows the measured Q as a function of the frequency ofthe embodiment 31 of the planar inductive component in accordance withthe invention. The maximum value of curve 31A is 15.8.

The measured improvement of Q_(max) is slightly below the calculatedimprovement of Q_(max). In the design 28, the distance between theelectroconductive material of a spiral pattern or two interlaced spiralpatterns is not the same for the embodiments 29, 30 and 31. For theembodiment 29 of a planar inductor in accordance with the state of theart, this distance is larger than for embodiment 30 of the planarinductive component in accordance with the invention comprising twoconcentric, interlaced spiral patterns, while for said embodiment thedistance is larger than for embodiment 31 of the planar inductivecomponent in accordance with the invention comprising four concentric,interlaced spiral patterns. The smaller said distance, the larger theparasitic capacitance between the turns is. The increase in saidparasitic capacitance causes the measured improvement in Q_(max) to beslightly below the calculated improvement in Q_(max).

FIG. 9A is a diagrammatic cross-sectional view of an embodiment of aplanar transformer 32 in accordance with the invention. This embodimentcomprises a first planar inductive component 33 in accordance with theinvention and a second planar inductive component 34 in accordance withthe invention. The main faces of the first and the second planarinductive component 33 and 34 extend parallel to each other. Theimaginary centers of the first and the second planar inductive component33 and 34 are situated on an axis 35 that extends perpendicularly toboth main faces. The first planar inductive component 33 is provided onthe substrate 21. The first and the second planar inductive component 33and 34 are separated from each other by one of the insulating layers22B. Apart from the above-mentioned differences in construction, bothplanar inductive components are built up in the same manner as theinductive component shown in FIG. 6A. The first planar inductivecomponent 33 forms a first winding of the transformer 32. The secondinductive planar component 34 forms a second winding of the transformer32.

By positioning the first and the second planar inductive component 33and 34 relative to each other, it is achieved that the mutual magneticcoupling is maximized. An advantage of the planar transformer realizedin this manner is that at the first winding and at the second winding,the current is equally distributed over the spiral patterns of the firstplanar inductive component 33 and also uniformly distributed over thespiral patterns of the second planar inductive component 34. Asexplained hereinabove, this homogenized current distribution results inlow ohmic losses at high frequencies. Therefore, the planar transformer32 is excellently suited for operation at high frequencies.

FIG. 9B is a diagrammatic cross-sectional view of a further embodimentof the planar transformer 32 in accordance with the invention. Thisembodiment is comparable to the embodiment shown in FIG. 9A. It differsfrom the embodiment shown in FIG. 9A in that the substrate 21, whichextends parallel to the main faces of the first and the second planarinductive component 33 and 34, is situated between the first and thesecond inductive component and hence does not only serve as a supportbut also as an electrically insulating layer. The embodiment shown inFIG. 9A is particularly suitable for application in integrated circuits,while the embodiment shown in FIG. 9B is particularly suitable forapplication, for example, in the field of switch-mode power supplies. Inthe frequency range associated with switch-mode power supplies, it isfavorable to realize such planar transformers using thin-film orthick-film technologies with, for example, a ceramic substrate 21 oneither side of which electroconductive thin-film or thick-film materialsare provided. This embodiment is also excellently suited for use onprinted circuit boards on either side of which electroconductive layersof, for example, copper are provided.

FIG. 9C is a diagrammatic cross-sectional view of a further embodimentof the planar transformer 32 in accordance with the invention. Thisembodiment is comparable to the embodiment shown in FIG. 9B. Theoutstanding difference relative to the embodiment of FIG. 9B resides inthat the planar transformer is provided with an envelope 26 of amagnetic material. The envelope comprises a first part 26A and a secondpart 26B. In applications where it is compatible with the technologyused, the use of the envelope of magnetic material has the advantage ofimproved magnetic coupling between the first winding formed by the firstinductive component 33 and the second winding formed by the inductivecomponent 34. For practical reasons, for example to reduce thereproducibility in mass production, it may be useful to provide a small,well-defined air gap 27 between the first part 26A and the second part26B.

1. A planar inductive component comprising: at least a first and asecond concentric planar inductor, which include, respectively, a firstelectroconductive circular spiral pattern and a second electroconductivecircular spiral pattern, the first electroconductive circular spiralpattern having a first end point and a second end point, and the secondelectroconductive circular spiral pattern having a first end point and asecond end point, characterized in that the first electroconductivecircular spiral pattern that belongs to the first concentric inductor,and the second electroconductive circular spiral pattern that belongs tothe second concentric inductor are interlaced and are respectivelypatterned in a radius that increases from an inner end to an outer end;the first end point and the second end point of the firstelectroconductive circular spiral pattern are electroconductivelyinterconnected, and the first electroconductive circular spiral patternis interrupted at the outside by a narrow slit so as to form a firstelectroconductive contact and a second electroconductive contact oneither side of the interruption; the first end point and the second endpoint of the second electroconductive circular spiral pattern areelectroconductively interconnected, and the second electroconductivecircular spiral pattern is interrupted at the outside by a narrow slitso as to form a first electroconductive contact and a secondelectroconductive contact on either side of the interruption.
 2. Aplanar inductive component as claimed in claim 1, characterized in thatthe planar inductors each comprise at least a first electroconductivespiral pattern and a second electroconductive spiral pattern that areseparated from each other by an electrically insulating layer and thatform a spiral pattern that is asymmetrical about a center point of theinductive component.
 3. A planar inductive component as claimed in claim1, characterized in that the first electroconductive contact of thefirst electroconductive spiral pattern is electroconductively connectedto the first electroconductive contact of the second electroconductivespiral pattern, and the second electroconductive contact of the firstelectroconductive spiral pattern is electroconductively connected to thesecond electroconductive contact of the second electroconductive spiralpattern so as to form a system of electrically interconnected inductorshaving identical electrical and magnetic properties.
 4. A planartransformer comprising a first planar inductive component and a secondplanar inductive component as claimed in claim 1, wherein the firstplanar inductive component and the second planar inductive component areseparated by means of an electrically insulating layer, and wherein thefirst planar inductive component forms a first winding of the planartransformer and the second planar inductive component forms a secondwinding of the planar transformer.
 5. The planar inductive component ofclaim 1, wherein the first concentric planar inductor is connected inparallel to the second concentric planar inductor.
 6. The planarinductive component of claim 1, wherein the first and second endpointsof the first concentric inductor are coplanar and respectively locatedat inner and outer portions of the first concentric inductor and areconnected by an electrical conductor extending over concentric spiralwindings of the inductor.
 7. A planar inductive component as claimed inclaim 1, characterized in that the first end point and the second endpoint of at least one of the electroconductive circular spiral patternsare respectively located at innermost and outermost portions of thecircular spiral pattern, the narrow slit being in an outermost portionof the circular pattern that is separated from and between the first andsecond end points, the first and second end points being connected by aninterconnect that extends across the spiral pattern from the innermostend point to the outermost end point.
 8. A planar inductive arrangementcomprising: first and second concentric and coplanar interlaced spiralinductors, each spiral inductor having a spiral conductor extendingspirally from a centermost end to an outermost end via an increasingradius, and contacts on opposing sides of a slit interruption at anoutside portion of an outermost spiral of the conductor, the slitinterruption interrupting the contiguity of the outermost spiral; andfor each inductor, an electrical interconnect that connects thecentermost end to the outermost end.
 9. The arrangement of claim 8,wherein the first and second concentric and coplanar interlaced spiralinductors are interlaced such that the spiral conductors alternatebetween a spiral conductor of the first inductor and a spiral conductorof the second inductor when moving, in the plane of the inductors, froman innermost spiral of the concentric spirals to an outermost spiral ofthe concentric spirals.
 10. The arrangement of claim 8, wherein thefirst and second concentric and coplanar interlaced spiral inductors arelaterally separated by an insulator and form a contiguous planar regionextending from the centermost end of the conductors to the outermost endof the conductors.
 11. The arrangement of claim 8, wherein the spiralsin each inductor have a surface that is coplanar with surfaces of theother spirals in the arrangement, and wherein the spirals have an axisthat is about perpendicular to the coplanar surfaces.
 12. Thearrangement of claim 8, wherein the concentric and coplanar interlacedspiral inductors have electrical and magnetic properties that are aboutidentical to one another.
 13. The arrangement of claim 8, wherein theconcentric and coplanar interlaced spiral inductors are connected inparallel.
 14. A planar inductive component comprising: at least a firstand a second concentric planar inductor, which include, respectively, afirst electroconductive circular spiral pattern and a secondelectroconductive circular spiral pattern that have an increasingradius, are interlaced, electroconductively interconnected by vias andseparated from each other by an electrically insulating layer, the firstelectroconductive circular spiral pattern having a first end point and asecond end point, and the second electroconductive circular spiralpattern having a first end point and a second end point, the first endpoint and the second end point of the first electroconductive circularspiral pattern being electroconductively interconnected, and the firstelectroconductive circular spiral pattern being interrupted at theoutside by a narrow slit so as to form a first electroconductive contactand a second electro conductive contact on either side of theinterruption, and the first end point and the second end point of thesecond electroconductive circular spiral pattern beingelectroconductively interconnected, and the second electroconductivecircular spiral pattern being interrupted at the outside by a narrowslit so as to form a first electroconductive contact and a secondelectroconductive contact on either side of the interruption.
 15. Aplanar inductive component of claim 14, wherein the first end point andthe second end point of at least one of the electroconductive circularspiral patterns are respectively located at innermost and outermostportions of the circular spiral pattern, the narrow slit being in anoutermost portion of the circular pattern that is separated from andbetween the first and second end points, the first and second end pointsbeing connected by an interconnect that extends across the spiralpattern from the innermost end point to the outermost end point.